1. Field of the Invention
The present invention relates to a photographing apparatus and photographing method. More particularly, the present invention relates to a photographing apparatus and photographing method which acquire desired fundus tomographic images by reflecting moving amounts of the fundus in tomographic fundus imaging in real time.
2. Description of the Related Art
Recently, OCT (Optical Coherence Tomography) apparatus capable of acquiring fundus tomographic images have been attracting attention. One of the contributing factors in attracting attention is the capability to noninvasively examine the internal structure of the fundus which cannot be observed with other apparatus. FD-OCT (Fourier Domain OCT) which has a proven track record in high-speed imaging serves the center of the market. The OCT apparatus incorporates a fundus camera and a SLO (Scanning Laser Ophthalmoscope) and thereby allows OCT images to be acquired around a desired location by displaying which area of the fundus to be OCT-scanned.
On the other hand, for the purposes of detection of minute tumors or abnormalities in early diagnosis and early treatment, there is demand for improvements in image quality of OCT images. To achieve high image quality, a technique related to an apparatus (National Publication of International Patent Application No. 2004-512125) which makes an OCT beam follow fundus movements, i.e., changes in fundus location resulting from eye ball movements has been disclosed.
Also, a technique for capturing SLO images and OCT images alternately is disclosed (Japanese Patent Application Laid-Open No. 2008-029467) in relation to the above-described OCT apparatus equipped with the SLO apparatus.
In the configuration disclosed in National Publication of International Patent Application No. 2004-512125, a device adapted to detect fundus movements is added to the OCT apparatus. The device acquires OCT images of a desired site by tracking the optic disk in the fundus and controlling an OCT scanner in real time.
Also, by capturing SLO images and OCT images alternately, the configuration disclosed in Japanese Patent Application Laid-Open No. 2008-029467 acquires the SLO images and OCT images while reducing the burden on the patient.
As a result of FD-OCT's speedup, it may take a shorter time to acquire OCT images than to acquire fundus movement information. This will be described with reference to FIG. 3. When the OCT beam O is moved to a desired location and measurements are started, a plurality of OCT images 311 to 322 is acquired while SLO images 301 to 304 are acquired to calculate positional information. In this case, there is a problem in that positional information corresponding to all the OCT images is not available.
High-speed tracking will solve the above problem as with the invention disclosed in National Publication of International Patent Application No. 2004-512125, but it becomes essential to add a special device dedicated to tracking, resulting in a size increase of the apparatus, and furthermore in the need for expensive parts such as a tracking scanner. Also, there is a problem of increased initial operations such as setting of a target to be tracked, resulting in an increased imaging time.
Also, the invention disclosed in Japanese Patent Application Laid-Open No. 2008-029467 has a problem in that since SLO images and OCT images are acquired alternately, imaging takes much time, which can cause long delay times in the case of real-time tracking, resulting in a large deviation from the fundus location.